In recent years, liquid crystal display devices have been widely used for liquid crystal televisions, monitors, mobile phones, and the like, for example, as flat panel displays that have advantages such as thinner-profile and lighter-weight than a conventional cathode ray tube. Such liquid crystal display devices are provided with an illumination device (backlight) that emits light and a liquid crystal panel that displays a desired image by serving as a shutter for light emitted from a light source in the illumination device.
The illumination device is mainly categorized into a direct-lighting type and an edge-lighting type depending on how the light source is arranged with respect to the liquid crystal panel, which is an object to be irradiated by light. In liquid crystal display devices that are used for mobile equipment such as mobile phones, laptop computers, and PDAs, for example, the edge-lighting type, which makes it easier to achieve a thinner-profile as compared with the direct-lighting type, is typically employed. That is, in the edge-lighting type illumination device, by disposing a light source on the side of a liquid crystal panel, a thinner-profile is achieved, and by using a light guide plate disposed such that a light-emitting surface thereof faces a non-display surface of the liquid crystal panel, light from the light source is provided to the liquid crystal panel.
Such an illumination device typically has optical sheets (optical members) such as a lens sheet (light collection sheet) and a diffusion sheet between the light guide plate and the liquid crystal panel. In the illumination device, these optical sheets are used to make the light emitted from the light guide plate brighter and more uniform before the light is emitted toward the liquid crystal panel as illumination light.
In the conventional illumination device, as described in Patent Document 1 below, for example, a technique of disposing optical sheets on a resin frame so as to prevent deformation or breakage of the optical sheets in a display section thereof even when the optical sheets undergo great mechanical stress such as drop impact has been disclosed. Specifically, in this conventional illumination device, a holding section was formed in the end portion of the optical sheets, and by placing the holding section of the optical sheets in a recess formed in the resin frame, the optical sheets were mounted to the resin frame. Also, in this conventional illumination device, at least one cut-out portion was formed in the optical sheets at a boundary between the display section and the holding section thereof, and even when great mechanical stress such as drop impact occurs, the effect of deformation caused by this mechanical stress can be significantly reduced by this cut-out portion, which made it possible to prevent deformation or breakage of the optical sheets in the display section thereof.